THROMBOPOIETIN IS SYNERGISTIC WITH OTHER HEMATOPOIETIC GROWTH-FACTORSAND PHYSIOLOGICAL PLATELET AGONISTS FOR PLATELET ACTIVATION IN-VITRO

Thrombopoietin (TPO) is the primary physiologic regulator of platelet production. The effect of TPO on platelet function, both alone and in combination with other hematopoietic growth factors, adenosine diphosp hate (ADP), and epinephrine, was investigated using fluorescent-labele d antibodies to the activation-dependent antigen CD62 (P-selectin) and flow cytometry. TPO stimulated CD62 expression on normal human platel ets, and this expression was completely inhibited by the soluble extra cellular domain of the TPO receptor, MPL. The growth factors granulocy te colony-stimulating factor (G-CSF) and erythropoietin (EPO), but not interleukin-3 (IL-3) or stem-cell factor (SCF), also stimulated plate let activation. The combination of EPO, SCF, ADP, and epinephrine with TPO were synergistic for platelet CD62 expression. These data further support a role for TPO in modulating platelet function. (C) 1997 Wile y-Liss, Inc.